1. Field of the Invention
This invention relates to a method for the continuous production of a cross-linked polymer. More particularly, this invention relates to a method for the continuous production of a water-containing gel polymer cross-linked by aqueous solution polymerization.
2. Description of the Prior Art
Heretofore, cross-linked polymers using acrylamide, acrylic acid or salts thereof as main components have been known for their ability to absorb and retain large volumes of water, effect ion exchange, and induce chelation and have found extensive utility in various applications as sanitary articles, soil conditioners for agronomic uses, dehydrants, ion-exchange resins and adsorbents. For the production of these cross-linked polymers, the method which comprises polymerizing an aqueous monomer solution as water-in-oil emulsified or suspended in a hydrophobic solvent and the method which comprises cast polymerizing an aqueous monomer solution have found recognition and acceptance. The method of water-in-oil emulsion polymerization and the method of water-in-oil suspnesion polymerization entail use of large volumes of organic solvent and, therefore, prove highly dangerous from the standpoint of prevention of accidents and pose a serious problem of possible exposure of workers to toxic effects of the organic solvent. The method which relies on the cast polymerization of an aqueous monomer solution is excellent over the two methods described above in the sense that it has no use for any organic solvent. This method nevertheless requires continual removal of heat of reaction during the course of polymerization and inevitably entails use of an intricate and expensive polymerization device. Further, in producing a cross-linked polymer in a dry state from the produced water-containing gel polymer by the removal of the water, there is essentially involved a step of finely dividing the water-containing gel polymer mechanically thereby increasing the surface area of the polymer enough for drying. In this case, the mechanical fine division of the water-containing gel polymer may be accomplished by cutting or extrusion, for example. In either case, the work of fine division of the polymer consumes a high amount of energy because the water-containing gel polymer possesses strong rubbery elasticity.
As a solution to the various problems described above, the inventors have proposed in Japanese Patent Laid-open No. SHO 57(1982)-34101 a method for the batchwise radical aqueous solution polymerization by the use of a vessel provided with a plurality of rotary stirring shafts. Although this method has succeeded in improving productivity and workability to some extent over the conventional methods, it still has much to be desired.
An object of this invention, therefore, is to provide a novel method for the continuous production of the cross-linked polymer.
Another object of this invention is to provide a method for the continuous production of a water-containing gel polymer cross-linked by aqueous solution polymerization.